1. Field of the Invention
The present invention relates to a pattern inspection method and a pattern inspection system and, more particularly, to a pattern inspection method and a pattern inspection system for examining a pattern formed on a substrate by using a photographic image of a semiconductor circuit and design data of the semiconductor circuit.
2. Background Art
In recent years, the development of semiconductor devices manufactured by finer patterning, having increased numbers of layers in multiplayer structure and complicated in logic has been pursued. In the present circumstances, it is extremely difficult to manufacture such semiconductor devices. As a result, the occurrence of defects coming from manufacturing processes tends to increase, and it is important to efficiently and correctly detect such defects and to identify manufacturing process problems.
The kinds of possible defects from a manufacturing process include deformation, breakage and short circuit of a pattern. Such defects can be detected by comparison with a reference pattern having an ideal shape. More specifically, an operator selects a pattern element having an ideal shape from patterns formed on a wafer. An image of the pattern element is taken (as a reference pattern). Subsequently, an image of a pattern to be examined is taken; the positions of the image of the object to be examined and the reference pattern element are adjusted; and a difference therebetween is computed. If the pattern to be examined includes a defect, luminance information at a position corresponding to the defect differs from luminance information about the reference pattern element and, correspondingly, the amount of difference is increased. By utilizing this nature, a position at which a differential value equal to or larger than a certain value is exhibited is detected as a defect position.
Such inspection is carried out with a review scanning electron microscope (review SEM) such as one disclosed in JP Patent Application No. 11-343094 (1999). The review SEM irradiates a specimen with an electron beam and performs the above-described inspection by using an image formed by using secondary electrons and backscattered electrons emitted from the specimen surface. An ordinary review SEM has a secondary electron detector for detecting secondary electrons and a backscattered electron detector for detecting backscattered electrons. Signals from the respective detectors are formed as a secondary electron image and a backscattered electron image. Each of the electron images is seen in different ways due to the difference between the characteristics of electrons used to form the images. The secondary electron image is suitable for observation and inspection of a pattern configuration, while the backscattered electron image is suitable for observation and inspection of a three-dimensional configuration of a pattern. However, the backscattered electron detector cannot detect backscattered electrons from a portion of the pattern element shielded with the major portion of the pattern element as seen from the position at which the backscattered electron detector is disposed. Therefore, three dimensional configuration of the whole pattern element cannot be expressed from a backscattered electron image formed by one backscattered electron detector. To enable observation of details of a three-dimensional configuration of a pattern, therefore, backscattered electron detectors are disposed at very small intervals so as to surround a specimen, and a plurality of backscattered electron images emitted from the pattern are formed. In an ordinary review SEM, however, two or three backscattered electron detectors are provided by considering the equipment cost and the installation area and are disposed so as to surround a specimen to obtain a plurality of backscattered electron images. Images used for pattern inspection are selectively used according to inspection purposes in such a manner that ordinary pattern inspection is performed by inspection through secondary electron images while inspection of a three-dimensional configuration of a pattern or a defect is performed by using backscattered electron images.
In a case where a pattern with openings such as holes is inspected, emission of secondary electrons from a hole area is weak. In such a case, an inspection method such as disclosed in JP Patent Publication (Kokai) No. 2000-260380 is used in which a backscattered electron image is blended at a certain ratio with a secondary electron image in an image of a hole area.
A mode of inspection using a reference pattern taken as an image as disclosed in JP Patent Application No. 11-343094 (1999) and JP Patent Publication (Kokai) 2000-260380 requires a user operation to register the reference pattern and, therefore, entails a problem in that a considerably long time is required for the reference pattern registering operation if patterns of various configurations are inspected.
Trials have therefore been made to automate the reference pattern registering operation and reduce the inspection time by adopting a method of using design data for a semiconductor device for a reference pattern and detecting a defect by comparing the design data and a pattern. For example, JP Patent Publication (Kokai) No. 2005-277395 discloses detection of a defect through comparison between design data and a pattern. More specifically, a manufactured semiconductor structure is irradiated with an electron beam; a contour line in a pattern is extracted by image processing from a secondary electron image formed by detecting secondary electrons emitted from the surface of the semiconductor structure; the contour line and the corresponding shape according to design data is compared with each other; and a portion of the pattern having a difference in shape is detected as a defect.